In polysilicon-emitter bipolar technologies, the emitter results from a deposition of polysilicon which can be carried out in a conventional oven followed by a doping operation. As a variant, the emitter may be doped in situ in a chemical vapor deposition (CVD) reactor. In both cases, an oxide layer is present at the emitter/base interface. This layer limits the hole current in the base (injected electrons continue to flow due to the tunnel effect). This helps to obtain a sufficient current gain (I.sub.c /I.sub.b).
However, these polysilicon-emitter transistors have certain drawbacks. First of all, they exhibit low-frequency noise which results in low-frequency fluctuations in the transistor current. This is even more troublesome in the case of radio frequency circuits incorporating such transistors for separating two close carriers. Furthermore, this is troublesome in the case of oscillators. Moreover, the dimensional characteristics of the oxide layer at the base/polysilicon-emitter interface have an influence on the static parameters of the transistor, especially its gain. However, it is particularly difficult to guarantee identical characteristics for oxide interfaces of all the transistors of several batches, this being especially so when the surface of the emitters varies. Consequently, it is particularly difficult to obtain uniform characteristics in all the transistors produced, whatever the surface of their emitter.